Research On Adsorption Of Hexavalent Chromium And Congo Red In Aqueous Solutions Onto Modified Graphene Oxide/Chitosan Composite Materials

Hexavalent chromium?Cr????is one of the eight kinds of chemicals which are most harmful for human health,as well as one of the five heavy metals which are most toxic for human.Congo red?CR?is not only a threat for human people but for water quality and aquatic life.Grapheme oxide?GO?is widely used in water treatment field in recent years due to its lage specific surface area and abundant oxygen containing functional groups.Chitosan?CS?containing a large number of amino and hydroxyl groups,is considered the most promising biological adsorbent in water treatment field,what'more,CS can be obtained from wide sources.It is biocompatible and biodegradable as well.However,the hydrophilicity of GO makes it difficult to separation from aqueous solution,CS is soluble in acid medium,which leds to the loss of CS in solution and not easy to recycle.The drawback limits their practical application.In this study,a novel adsorbent has been successfully prepared by modifying graphene oxide/chitosan composite with disodium ethylenediaminetetraacetate?EDTA-2Na??GEC?.The morphology and structure of the composite material were characterized by various methods.GEC was used as adsorbent for Cr???and CR removing in aqueous solutions.Batch adsorption experiments were carried out to evaluate the effects of contact time,pH,dosage and temperature on the adsorption of Cr???and CR by GEC.The adsorption kinetics,isotherm and thermodynamoic were analized.Some experiments were conducted to evaluate the regeneration performance of GEC.The results show that GO and CS spread out in GEC composite material,not only making GO easy separated from the aqueous solution,also improving the stability of the CS in acid solution and the adsorption ability of GEC.The results indicate that the adsorption of Cr???on GEC was highly pH-dependent,with the highest adsorption capacity?86.17 mg/g?occurring at pH 2.The kinetics of adsorption exhibited pseudo-second-order behavior.The adsorption data were well described by the Freundlich isotherm model.The adsorption capacity increased with increasing temperature.The calculated thermodynamic parameters indicate that the adsorption is a spontaneous,endothermic and feasible process.The further regeneration experiments showed the adsorption capacity of GEC for Cr???decreased 5% after 7 times reuse.GEC have high capacity for adsorption of CR in a large range of pH value.The kinetics of adsorption exhibited pseudo-second-order behavior.The adsorption data were well described by the Langmuir isotherm model.The adsorption capacity increased with increasing temperature.The calculated thermodynamic parameters indicate that the adsorption is a spontaneous,endothermic and feasible process.The maximum adsorption capacity of GEC was 175.43 mg·g^-1 at 298 K.Further regeneration experiments showed the adsorption capacity of GEC for CR have no obvious change after 6 times reuse,indicating the potential of the as-prepared material for practical application.